How does transformer oil density change with temperature?

Transformer oil density decreases as temperature increases because the fluid expands. This affects mass to volume conversions, oil level readings, and conservator behavior, especially during load swings. For example, the same mass of oil occupies more volume at higher temperature, raising level in the conservator. That is why oil level indicators are typically interpreted with temperature, and why filling procedures reference a specific oil temperature. Always use the supplier density versus temperature curve for accurate calculations.